PHYS Biomechanics of Breathing - Week 1

Question 1

Boyle’s Law

Answer 1

P1V1 = P2V2 (in a closed system, any change in volume will result in a change in pressure).

Question 2

Chest movement direction, external intercostals…, ribs…, sternum… on inspiration.

Answer 2

Chest moves out & upwards (external intercostals contract, ribs elevate via lateral shaft, sternum flares w sup & ant movement).

Question 3

Chest movement direction, external intercostals…, ribs…, sternum… on expiration.

Answer 3

Chest moves down & inwards (external intercostals relax, ribs & sternum are depressed).

Question 4

Pleural effusion

Answer 4

Accumulation of fluid in pleural cavity.

Question 5

Empyema

Answer 5

Pus in pleural cavity.

Question 6

Pneumothorax

Answer 6

Air in pleural cavity.

Question 7

Haemothorax

Answer 7

Blood in the pleural cavity.

Question 8

Intrapleural pressure +ve or -ve

Answer 8

Always -ve. 756mmHg (-ve as Patm = 760mmHg)

Question 9

Breathing technique characteristic of pts with low lung compliance

Answer 9

Shallow breathing at a fast rate to ensure inspiration of an adequate volume.

Question 10

Lungs can expand & inflate due to:

Answer 10

Lung compliance & airway radius

Question 11

Lung compliance is determined by

Answer 11

Stretchability of the lung tissue & consistency of the lung tissue (collagen fibrils, elastin, fibroblast presence & surface tension of the air-fluid interface lining alveoli).

Question 12

4 factors affecting airway radius & consequences of each (i.e., bronchodilation/bronchoconstriction).

Answer 12

1. Vagal efferent nerves (ACh) -> bronchoconstriction
2. Sympathetic nerve supply (NA) -> bronchodilation
3. Circulating catecholamines (B receptors) -> bronchodilation
4. Inhaled stimuli (e.g., cigarettes, dust, cold air) -> reflex bronchoconstriction.

Question 13

When does surfactant production begin embryological development.

Answer 13

6-7mths gestation.

Question 14

Clinical examples of decreased lung compliance

Answer 14

Pulmonary fibrosis, ARDS.

Question 15

Clinical examples of increased lung compliance

Answer 15

COPD, emphysema.

Question 16

Character of lungs w low compliance

Answer 16

Stiff, difficult to inflate.

Question 17

Character of lungs w high compliance

Answer 17

Difficult to deflate, increased elastic recoil.

Question 18

Spirometry results corresponding to airway radius & lung and chest compliance

Answer 18

• Airway radius - look at the inspiratory and expiratory flow rates and the FEV1/FVC% (see below).
• Lung and chest compliance - look at the vital and total lung capacity, i.e. VC and TLC. We can measure VC with spirometry but not TLC.

Question 19

Reduced airway radius clinically corresponds to what presentation

Answer 19

Obstructive lung disorders (e.g., asthma, COPD).

Question 20

Reduced lung & chest compliance clinically corresponds to what presentation

Answer 20

Restrictive lung disorders (e.g., fibrosis).

Question 21

Normal range for FVC

Answer 21

> 75% - pt should be able to breath out >75% air in first 1 second of max expiration.

Question 22

Intrapleural vs intrapulmonary vs transmural pressures. State whether each is usually positive or negative.

Answer 22

Intrapleural pressure refers to pressure between parietal & visceral pleura - in pleural cavity. Pressure is -ve due to attempt to move parietal & visceral layers apart which is impossible due to pleural fluid between these two layers (like water between two glass microscope slides).
Intrapulmonary/transpulmonary/intra-alveolar pressure refers to the pressure inside the lungs.
Transmural pressure = intrapulmonary - intrapleural pressures.
+ve/-ve, -ve, always +ve.

Question 23

What 2 x forces are responsible for preventing alveolar collapse?

Answer 23

Surfactant action & transmural pressure gradient.

Question 24

Hyperinflation is associated with restrictive or obstructive?

Answer 24

Obstructive as the air can’t get Out -> hyperinflation.